I first saw Rosa sertata Rolfe var. multijuga Yu & Ku in 1996 at U.C. Berkeley Botanic Garden, Accession # 89.0424 collected in Sichuan Province, China. It was September and the rose was covered with smooth glossy orange-red hips. The hips were not moist or fleshy and beneath the thin skin the seeds were neatly arranged like segments of an orange. I happen to save that hip in my pocket and later sprouted a seedling which grew to become sertata var. multijuga just like its parent.
Later I discovered in the Flora of China, sertata var. multijuga is found only in one location in Sichuan Province, Dawu Xian or Dawn County on the Tibetan Plateau (called "The Roof of the World"), while Rosa sertata itself ranges over eastern China at a lower elevation from 4600 to 7200 feet. Twenty years later while surveying the Rosa at Quarryhill I encountered a striking but unidentified species, Accession # 2001.361E collected in Sichuan Province at 7800 feet of elevation. After careful study, I determined it was also a sertata var. multijuga.
The Chinese botanists, T.T. Yu and T.C. Ku who described and named var. multijuga in 1981 distinguish it from sertata by several features. Multijuga's leaflets number from 9 to 15 with a leaflet margin that is "apically aristate" i.e. having bristles. Rosa sertata has less leaflets, from 7 to 11 without bristles on the leaflet teeth.
Yu and Ku's epithet, multijuga means long yokes. Combined with the epithet, sertata, the Latin translates to "the Rose with fine leaves in long strands." But it's also possible they're referring to the multiple "yoked" flower clusters all along the stems, like festive garlands when blooming.